Keyboards for electronic products such as calculators have employed a variety of different switching elements as designers have attempted to make the keyboards less expensive, more reliable and more pleasing to use. One type of commonly used switch element is the metal snap disc which comprises a metal disc that has been formed in the shape of a spherical segment. When force is applied to the center of the disc, the disc will deflect while presenting increasing resistance to deflection until a point is reached when the resistive force presented by the disc will suddenly decrease with increased deformation, and the disc will appear to the user to "snap." This action of the disc has been likened to the action of an oil can or a toy "cricket."
Numerous prior art references show snap discs as keyboard switch elements, such as U.S. Pat. No. 3,684,842 by Boulanger granted Aug. 15, 1972 and U.S. Pat. No. 3,967,084 by Pounds granted June 29, 1976. In these patents, a substrate such as a printed circuit board is provided to support the discs and conductors are provided on the substrate to make contact with the discs. Usually the conductors are arranged so that the discs form a bridging switch contact between two conductors. One of the disadvantages of using snap discs as switch elements is that the discs must be placed one at a time on the supporting substrate during assembly of the keyboard. This procedure is time consuming and error prone, leading to undesirably high assembly costs. Various means of solving such problems have been proposed. One such proposal comprises forming a plurality of discs in a single sheet of material, as in U.S. Pat. No. 3,590,195 by Driver granted June 29, 1971 and U.S. Pat. No. 3,643,041 by Jackson granted Feb. 15, 1972. Another proposal comprises forming the discs out of a single sheet of material and then removing some of the material, leaving the discs joined by parallel strips of material as in U.S. Pat. No. 3,952,174 by Boulanger et al granted Apr. 20, 1976. Further examples of keyboards with metal snap type switch elements and keys for actuating them are shown in U.S. Pat. No. 3,941,953 by Misson et al. granted Mar. 2, 1976 and U.S. Pat. No. 3,916,135 by Holden et al. granted Oct. 28, 1975.
The aforementioned approaches to improved speed of assembly are offset by a reduction in the snap feel or tactile response provided by the disc. This reduction occurs in part because the disc is constrained by the surrounding material. In addition, these discs are commonly actuated directly by a plunger type key that rests directly on the top of the disc. When such a key is actuated, the key travel is relatively short and the feel is relatively harsh. Furthermore, the cost of tooling is undesirably high for the type of keyboard with the discs formed in a single sheet of material.